1. Field of the Invention
The present invention relates generally to a mobile communication system, and in particular, to a method and apparatus for performing measurement on neighboring cells for cell selection or cell reselection and handover.
2. Description of the Related Art
The Universal Mobile Telecommunication Service (UMTS) system is a 3rd generation asynchronous mobile communication system that uses Wideband Code Division Multiple Access (W-CDMA) and is based on Global System for Mobile communications (GSM) and General Packet Radio Services (GPRS), both of which are European mobile communication systems. In 3rd Generation Partnership Project (3GPP) in charge of UMTS standardization, a Long Term Evolution (LTE) system is now under discussion as the next generation mobile communication system of the UMTS system. LTE is a technology for implementing high-speed packet-based communication having a transfer rate of a maximum of 100 Mbps, aimed at its commercialization in around 2010. To this end, several schemes are under discussion, and they include, for example, a scheme of reducing the number of nodes situated in the communication path by simplifying a configuration of the network, and another scheme of maximally approximating wireless protocols to wireless channels.
FIG. 1 illustrates an exemplary configuration of an Evolved UMTS mobile communication system.
Referring to FIG. 1, an Evolved UMTS Radio Access Network (E-UTRAN or E-RAN) 110 is simplified to a 2-node configuration of evolved Node Bs (eNBs) 120, 122, 124, 126 and 128, and anchor nodes 130 and 132. A User Equipment (UE) 101, also known as a terminal, accesses the Internet Protocol (IP) network by means of E-RANs 110 and 112. The eNBs 120 to 128, which correspond to the legacy Node Bs of the UMTS system, are connected to the UE 101 over wireless channels.
Compared with the legacy Node Bs, the eNBs 120 to 128 perform a complex function. In LTE, since all user traffics, including real-time services such as Voice over IP (VoIP), are serviced through a shared channel, there is a need for a device for gathering status information of UEs to perform scheduling, and the eNBs 120 to 128 serve as the device. Generally, one eNB controls a plurality of cells. In addition, the eNB performs Adaptive Modulation & Coding (AMC) that adaptively determines a modulation scheme and a channel coding rate according to the channel status of UEs.
Like in High Speed Downlink Packet Access (HSDPA), High Speed Uplink Packet Access (HSUPA) and/or Enhanced Dedicated Channel (E-DCH) services of UMTS, Hybrid Automatic Repeat reQuest (HARQ) is performed between the eNBs 120 to 128 and the UE 101 even in LTE, and since various Quality-of-Service (QoS) requirements cannot be satisfied only with HARQ, outer ARQ in an upper layer can be performed between the UE 101 and the eNBs 120 to 128. HARQ, a technique for soft-combining the previously received data with its retransmitted data without discarding the previously received data to increase a reception success rate, is used for increasing transmission efficiency in high-speed packet communication such as HSDPA and EDCH services. To implement the transfer rate of a maximum of 100 Mbps, LTE is expected to use Orthogonal Frequency Division Multiplexing (OFDM) as a wireless access technology in a 20-MHz bandwidth.
In such next generation mobile communication systems, there is a need for a measurement scheme for neighboring cells for cell selection or cell reselection and handover.